A Bronx teen set to join the Navy was gunned down trying to play peacemaker, cops and relatives said yesterday.

Victor Maldonado, 19, was visiting a friend when he encountered two women arguing in a building on Heath Avenue in Kingsbridge at about 10:20 p.m. Monday.

“One of the girls got upset because she didn’t say thank you for holding the door,” the victim’s aunt Valerie Torres said. “He tried to break it up. One of the girls came out and told him, ‘I’m going to get my brother!’ ”

A man soon showed up and opened fire.

“My brother was killed for such a stupid reason,” said Maldonado’s sister, Nayiliana DeJesus, 15.

“He was so loving and kind. He had a good life ahead of him.”

Maldonado was set to take his Navy physical next week.

“My uncle and grandfather were in the Navy, too. He wanted to be just like them,” Nayiliana said.